Ozone is currently used in many European countries for purposes of water purification, and is used worldwide for purposes of sterilization in environments such as hospitals, movie theaters, and fitness centers. In the prior art, large volumes of ozone are typically produced through the use of corona discharge generators wherein a corona is discharged into pure oxygen. These generators require the use of pure oxygen, in that the discharge of a corona into air facilitates the creation of equal quantities of ozone and poisonous nitrogen dioxide which, if mixed with water vapor, creates nitric acid. As such, prior art corona discharge generators for producing large volumes of ozone require the use of auxiliary systems which produce pure oxygen from air, to provide a constant source of pure oxygen. As will be recognized, the use of the prior art corona discharge generators is extremely costly and inefficient in view of the requirement that pure oxygen be used therewith.
In view of the shortcomings associated with the use of corona discharge generators, there has also been developed in the prior art a method of producing more clean and pure ozone through the use of ultraviolet radiation having wavelengths below 220 nm. In prior art systems using this alternative ozone production method, the ultraviolet radiation is generated through the use of low-pressure mercury lamps powered with AC voltage through common fluorescent ballasts. Examples of these types of ultraviolet radiation ozone generating systems are disclosed in U.S. Pat. Nos. 2,042,963; 2,088,544; and 5,387,400. Though these systems present advantages over the corona discharge generators they also possess certain deficiencies which detract from their overall utility. Such deficiencies include the a very large size due to the need to include a separate ballast for each mercury lamp, and the high power consumption associated with the inclusion of many ballasts.
It has also been determined in the prior art that the efficiency of excitation of electric discharge in a mercury lamp can be increased up to two times by replacing the AC or DC excitation with microwave excitation. In addition to increasing discharge efficiency, the use of microwave excitation also eliminates the need for the ballasts to power each of the individual mercury lamps. The use of microwaves to power efficient, medium pressure mercury lamps is disclosed in U.S. Pat. Nos. 3,872,349; 3,911,318; and 4,042,850. In these particular references, microwave cavities are used in conjunction with microwave powered deep ultraviolet light sources. However, the microwave cavities disclosed in these references operate on fundamental or near fundamental cavity modes. These type of mode structures make it impossible to simultaneously excite a large number of lamps uniformly due to the inclusion of a very clearly defined, non-homogeneous standing wave electric field distribution inside the microwave cavity. Though the multi-mode cavities widely used in conventional microwave ovens provide homogeneous electric field distribution inside the cavity, they do not provide the critical optimal electric field strength absolutely necessary for the efficient excitation of low pressure mercury lamps for the efficient generation of ozone.
The present invention overcomes the deficiencies associated with the prior art by defining the critical conditions which interrelate the geometry of the microwave cavity, the individual lamp dimensions, the microwave cavity volume, and the microwave power of the magnetron generator for the efficient, homogenous excitation in the same microwave cavity of from one to thousands of ozone producing lamps. In the present invention, clean and pure ozone is generated with up to two times less energy consumption than prior art AC/DC mercury lamp ozone generators including the same number of lamps. In this respect, the present invention provides a powerful, compact, low-cost and reliable ultraviolet ozone generator for the production of clean ozone, free from nitrogen oxides, using standard, ozone producing lamps.